IUD's can be inserted during any time of menstrual cycle.
But usually it is inserted during or just after the menstrual cycle, this is because chance of pregnancy
during menses or just after menses is almost negligible.
So that inserting IUD's in pregnant uterus
can be avoided
And also during menses there is some other advantages like chance of infection is also less.
In India, it is usually done just after menses. But Gync of some other countries prefer mid cycle since it is easier to insert due to cervix